diff --git a/lib/libc/stdlib/div.c b/lib/libc/stdlib/div.c
--- a/lib/libc/stdlib/div.c
+++ b/lib/libc/stdlib/div.c
@@ -41,34 +41,6 @@
 
 	r.quot = num / denom;
 	r.rem = num % denom;
-#if !defined(__STDC_VERSION__) || (__STDC_VERSION__ < 199901L)
-	/*
-	 * The ANSI standard says that |r.quot| <= |n/d|, where
-	 * n/d is to be computed in infinite precision.  In other
-	 * words, we should always truncate the quotient towards
-	 * 0, never -infinity.
-	 *
-	 * Machine division and remainer may work either way when
-	 * one or both of n or d is negative.  If only one is
-	 * negative and r.quot has been truncated towards -inf,
-	 * r.rem will have the same sign as denom and the opposite
-	 * sign of num; if both are negative and r.quot has been
-	 * truncated towards -inf, r.rem will be positive (will
-	 * have the opposite sign of num).  These are considered
-	 * `wrong'.
-	 *
-	 * If both are num and denom are positive, r will always
-	 * be positive.
-	 *
-	 * This all boils down to:
-	 *	if num >= 0, but r.rem < 0, we got the wrong answer.
-	 * In that case, to get the right answer, add 1 to r.quot and
-	 * subtract denom from r.rem.
-	 */
-	if (num >= 0 && r.rem < 0) {
-		r.quot++;
-		r.rem -= denom;
-	}
-#endif
+
 	return (r);
 }
diff --git a/lib/libc/stdlib/imaxdiv.c b/lib/libc/stdlib/imaxdiv.c
--- a/lib/libc/stdlib/imaxdiv.c
+++ b/lib/libc/stdlib/imaxdiv.c
@@ -36,11 +36,6 @@
 
 	retval.quot = numer / denom;
 	retval.rem = numer % denom;
-#if !defined(__STDC_VERSION__) || (__STDC_VERSION__ < 199901L)
-	if (numer >= 0 && retval.rem < 0) {
-		retval.quot++;
-		retval.rem -= denom;
-	}
-#endif
+
 	return (retval);
 }
diff --git a/lib/libc/stdlib/ldiv.c b/lib/libc/stdlib/ldiv.c
--- a/lib/libc/stdlib/ldiv.c
+++ b/lib/libc/stdlib/ldiv.c
@@ -43,11 +43,6 @@
 
 	r.quot = num / denom;
 	r.rem = num % denom;
-#if !defined(__STDC_VERSION__) || (__STDC_VERSION__ < 199901L)
-	if (num >= 0 && r.rem < 0) {
-		r.quot++;
-		r.rem -= denom;
-	}
-#endif
+
 	return (r);
 }
diff --git a/lib/libc/stdlib/lldiv.c b/lib/libc/stdlib/lldiv.c
--- a/lib/libc/stdlib/lldiv.c
+++ b/lib/libc/stdlib/lldiv.c
@@ -36,11 +36,6 @@
 
 	retval.quot = numer / denom;
 	retval.rem = numer % denom;
-#if !defined(__STDC_VERSION__) || (__STDC_VERSION__ < 199901L)
-	if (numer >= 0 && retval.rem < 0) {
-		retval.quot++;
-		retval.rem -= denom;
-	}
-#endif
+
 	return (retval);
 }
diff --git a/share/mk/bsd.sys.mk b/share/mk/bsd.sys.mk
--- a/share/mk/bsd.sys.mk
+++ b/share/mk/bsd.sys.mk
@@ -12,15 +12,7 @@
 
 CSTD?=		gnu17
 
-.if ${CSTD} == "c89" || ${CSTD} == "c90"
-CFLAGS+=	-std=iso9899:1990
-.elif ${CSTD} == "c94" || ${CSTD} == "c95"
-CFLAGS+=	-std=iso9899:199409
-.elif ${CSTD} == "c99"
-CFLAGS+=	-std=iso9899:1999
-.else # CSTD
 CFLAGS+=	-std=${CSTD}
-.endif # CSTD
 
 .if !empty(CXXSTD)
 CXXFLAGS+=	-std=${CXXSTD}
diff --git a/sys/conf/kern.mk b/sys/conf/kern.mk
--- a/sys/conf/kern.mk
+++ b/sys/conf/kern.mk
@@ -276,17 +276,7 @@
 
 CSTD?=		gnu17
 
-.if ${CSTD} == "k&r"
-CFLAGS+=        -traditional
-.elif ${CSTD} == "c89" || ${CSTD} == "c90"
-CFLAGS+=        -std=iso9899:1990
-.elif ${CSTD} == "c94" || ${CSTD} == "c95"
-CFLAGS+=        -std=iso9899:199409
-.elif ${CSTD} == "c99"
-CFLAGS+=        -std=iso9899:1999
-.else # CSTD
-CFLAGS+=        -std=${CSTD}
-.endif # CSTD
+CFLAGS+=	-std=${CSTD}
 
 # Please keep this if in sync with bsd.sys.mk
 .if ${LD} != "ld" && (${CC:[1]:H} != ${LD:[1]:H} || ${LD:[1]:T} != "ld")
diff --git a/usr.bin/lex/initscan.c b/usr.bin/lex/initscan.c
--- a/usr.bin/lex/initscan.c
+++ b/usr.bin/lex/initscan.c
@@ -28,11 +28,6 @@
 #ifndef FLEXINT_H
 #define FLEXINT_H
 
-/* C99 systems have <inttypes.h>. Non-C99 systems may or may not. */
-
-#if defined(__FreeBSD__) || \
-    (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 199901L)
-
 /* C99 says to define __STDC_LIMIT_MACROS before including stdint.h,
  * if you want the limit (max/min) macros for int types. 
  */
@@ -47,48 +42,6 @@
 typedef uint16_t flex_uint16_t;
 typedef int32_t flex_int32_t;
 typedef uint32_t flex_uint32_t;
-#else
-typedef signed char flex_int8_t;
-typedef short int flex_int16_t;
-typedef int flex_int32_t;
-typedef unsigned char flex_uint8_t; 
-typedef unsigned short int flex_uint16_t;
-typedef unsigned int flex_uint32_t;
-
-/* Limits of integral types. */
-#ifndef INT8_MIN
-#define INT8_MIN               (-128)
-#endif
-#ifndef INT16_MIN
-#define INT16_MIN              (-32767-1)
-#endif
-#ifndef INT32_MIN
-#define INT32_MIN              (-2147483647-1)
-#endif
-#ifndef INT8_MAX
-#define INT8_MAX               (127)
-#endif
-#ifndef INT16_MAX
-#define INT16_MAX              (32767)
-#endif
-#ifndef INT32_MAX
-#define INT32_MAX              (2147483647)
-#endif
-#ifndef UINT8_MAX
-#define UINT8_MAX              (255U)
-#endif
-#ifndef UINT16_MAX
-#define UINT16_MAX             (65535U)
-#endif
-#ifndef UINT32_MAX
-#define UINT32_MAX             (4294967295U)
-#endif
-
-#ifndef SIZE_MAX
-#define SIZE_MAX               (~(size_t)0)
-#endif
-
-#endif /* ! C99 */
 
 #endif /* ! FLEXINT_H */
 
diff --git a/usr.bin/lex/initskel.c b/usr.bin/lex/initskel.c
--- a/usr.bin/lex/initskel.c
+++ b/usr.bin/lex/initskel.c
@@ -466,11 +466,6 @@
   "#ifndef FLEXINT_H",
   "#define FLEXINT_H",
   "",
-  "/* C99 systems have <inttypes.h>. Non-C99 systems may or may not. */",
-  "",
-  "#if defined(__FreeBSD__) || \\",
-  "    (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 199901L)",
-  "",
   "/* C99 says to define __STDC_LIMIT_MACROS before including stdint.h,",
   " * if you want the limit (max/min) macros for int types. ",
   " */",
@@ -485,48 +480,6 @@
   "typedef uint16_t flex_uint16_t;",
   "typedef int32_t flex_int32_t;",
   "typedef uint32_t flex_uint32_t;",
-  "#else",
-  "typedef signed char flex_int8_t;",
-  "typedef short int flex_int16_t;",
-  "typedef int flex_int32_t;",
-  "typedef unsigned char flex_uint8_t; ",
-  "typedef unsigned short int flex_uint16_t;",
-  "typedef unsigned int flex_uint32_t;",
-  "",
-  "/* Limits of integral types. */",
-  "#ifndef INT8_MIN",
-  "#define INT8_MIN               (-128)",
-  "#endif",
-  "#ifndef INT16_MIN",
-  "#define INT16_MIN              (-32767-1)",
-  "#endif",
-  "#ifndef INT32_MIN",
-  "#define INT32_MIN              (-2147483647-1)",
-  "#endif",
-  "#ifndef INT8_MAX",
-  "#define INT8_MAX               (127)",
-  "#endif",
-  "#ifndef INT16_MAX",
-  "#define INT16_MAX              (32767)",
-  "#endif",
-  "#ifndef INT32_MAX",
-  "#define INT32_MAX              (2147483647)",
-  "#endif",
-  "#ifndef UINT8_MAX",
-  "#define UINT8_MAX              (255U)",
-  "#endif",
-  "#ifndef UINT16_MAX",
-  "#define UINT16_MAX             (65535U)",
-  "#endif",
-  "#ifndef UINT32_MAX",
-  "#define UINT32_MAX             (4294967295U)",
-  "#endif",
-  "",
-  "#ifndef SIZE_MAX",
-  "#define SIZE_MAX               (~(size_t)0)",
-  "#endif",
-  "",
-  "#endif /* ! C99 */",
   "",
   "#endif /* ! FLEXINT_H */",
   "",